pyrophosphate and beryllium-fluoride

The structure of the magnesium pyrophosphate complex of the truncated head of Dictyostelium myosin has been determined by molecular replacement at 2.7 A resolution and refined to a crystallographic R-factor of 16.0%. The crystals belong to the orthorhombic space group P2(1)2(1)2, where a = 105.2 A, b = 182.1 A, and c = 54.5 A. The conformation of the protein around the magnesium pyrophosphate is very similar to that seen when magnesium ADP-beryllium fluoride binds in the active site. The latter complex mimics the binding of ATP prior to hydrolysis. The pyrophosphate molecule occupies the beta- and gamma-phosphate sites, where the two phosphorus atoms are in the same positions as the beta-phosphate and the BeFx moiety of the beryllium fluoride-trapped ADP. The surrounding active site residues are almost perfectly superimposable in the two structures and the hydrogen-bonding interactions that the PPi makes with the protein are essentially identical. The similarity between the MgPPi and MgADP.BeFx complex with S1Dc suggests that the conformational change, which occurs when ATP binds to actomyosin and which reduces the affinity of myosin for actin, is caused by the binding of the gamma- and beta-phosphate groups of the nucleotide. This then implies that the role of the remainder of the substrate is to increase the binding affinity for myosin and thus to drive the equilibrium toward dissociation of myosin from actin.

Topics: Adenosine Diphosphate; Amino Acid Sequence; Animals; Beryllium; Binding Sites; Crystallography, X-Ray; Dictyostelium; Diphosphates; Fluorides; Magnesium Compounds; Models, Molecular; Molecular Sequence Data; Molecular Structure; Myosins; Protein Conformation; Protein Folding

The effect of phosphate analogs (pyrophosphate, aluminofluoride and beryllofluoride complexes) on the reactivation of apobromoperoxidase by vanadate was studied. P2O7(4-) inhibited the reactivation in the millimolar range. Of the different aluminofluoride complexes, only AlF4- was inhibitory. In addition, BeF4(2-) also appeared to bind with high affinity to the apobromoperoxidase, thus inhibiting the reactivation very strongly. The inhibition observed supports a mechanism in which the fluorometallic complexes act as analogs of vanadate and bind accordingly to the apobromoperoxidase.

Topics: Aluminum; Aluminum Compounds; Beryllium; Diphosphates; Enzyme Activation; Fluorides; Peroxidases; Phaeophyceae